High areal density tape format and head

ABSTRACT

A magnetic recording tape according to one embodiment includes at least about eight data bands, wherein each data band is defined between a pair of adjacent servo tracks, each pair of adjacent servo tracks defining only a single data band therebetween. One of the servo tracks has data encoded therein, the data including data for encryption. A magnetic recording tape according to another embodiment includes a plurality of servo tracks, each servo track comprising a series of magnetically defined bars. An average height of the bars is less than about 50 microns. About eight to about twenty six data bands are present on the tape. A tape supply cartridge according to various embodiments has a magnetic recording tape as described herein.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/460,430, filed Apr. 30, 2012; which is a continuation of U.S. patentapplication Ser. No. 12/987,750, filed Jan. 10, 2011; which iscontinuation of U.S. Pat. No. 7,952,832, granted May 31, 2011; which isa divisional of U.S. Pat. No. 7,791,834, granted Sep. 7, 2010, from allof which priority is claimed and which are herein incorporated byreference.

BACKGROUND

The present invention relates to tape-based data storage systems, andmore particularly, this invention relates to a tape-based data storagesystem, and components thereof, having a reduced writer pitch.

Business, science and entertainment applications depend upon computingsystems to process and record data. In these applications, large volumesof data are often stored or transferred to nonvolatile storage media,such as magnetic discs, magnetic tape cartridges, optical diskcartridges, floppy diskettes, or floptical diskettes. Typically,magnetic tape is the most economical, convenient, and secure means ofstoring or archiving data.

Storage technology is continually pushed to increase storage capacityand storage reliability. Improvement in data storage capacities inmagnetic storage media, for example, has resulted from improved mediummaterials, improved error correction techniques and decreased areal bitsizes. The data capacity of half-inch magnetic tape, for example, iscurrently measured in hundreds of gigabytes.

The improvement in magnetic medium data storage capacity arises in largepart from improvements in the magnetic head assembly used for readingand writing data on the magnetic storage medium. A major improvement intransducer technology arrived with the magnetoresistive (MR) sensororiginally developed by the IBM® Corporation. Later sensors using theGMR effect were developed. AMR and GMR sensors transduce magnetic fieldchanges to resistance changes, which are processed to provide digitalsignals. AMR and GMR sensors offer signal levels higher than thoseavailable from conventional inductive read heads for a given read sensorwidth and so enable smaller reader widths and thus more tracks per inch,and thus higher data storage density. Moreover, the sensor output signaldepends only on the instantaneous magnetic field intensity in thestorage medium and is independent of the magnetic fieldtime-rate-of-change arising from relative sensor/medium velocity. Inoperation the magnetic storage medium, such as tape or a magnetic disksurface, is passed over the magnetic read/write (R/W) head assembly forreading data therefrom and writing data thereto.

When a tape is written to, the span of data just written is the span ofthe head elements. However, any expansion and contraction of the tapeprior to reading results in an expansion or contraction of the spacebetween data tracks and thus the data span. Present tapes typicallyexpand and contract by approximately 1 part in 1000, or 0.1%.

In current Linear Tape Open (LTO) systems, the heads include servoreaders that are approximately 3 mm apart. The tape media also includesservo tracks having a spacing of about 3 mm, thereby defining data bandsof about 3 mm. A 0.1% expansion over 3 mm results in about 3 micrometersof expansion for a data band. Accordingly, the data tracks themselvesmust be greater than the reader widths plus 3 micrometers or thereadback will suffer from expansion- or contraction-inducedmisregistration. Accordingly, current tape formats are reaching theirlimits as far as increasing track density is concerned. To illustrate,consider the following example.

In current tape head products, read sensor width is chosen to be ½ thetrack width on the tape. Assume that the tracks are 12 micrometers wide.The sensor is then 6 microns wide. If at the outer tracks, there are 3micrometers of misregistration, then the readers over the outer databands may be riding along the edge of the data band. Then the reader maycome off the track due to uncompensated lateral tape excursions.Accordingly, the track widths (in this example) cannot be made smallerwithout increased risk of misreads due to tape wobble.

One method for compensating for tape lateral expansion and contractionis statically rotating the head and then making small angularadjustments to keep the readers/writers in the head aligned to tracks onthe tape. However, the static rotation leads to skew-relatedmisregistration and is generally complex and difficult to implement. Forexample tilted heads must be constructed so as not to steer tape, etc.

Another proposed solution attempts to control the tape width bycontrolling tape tension. However, this method works over a limitedrange only, and generally does not provide enough control.

BRIEF SUMMARY

A magnetic recording tape according to one embodiment includes at leastabout eight data bands, wherein each data band is defined between a pairof adjacent servo tracks, each pair of adjacent servo tracks definingonly a single data band therebetween. One of the servo tracks has dataencoded therein, the data including data for encryption.

A magnetic recording tape according to another embodiment includes aplurality of servo tracks, each servo track comprising a series ofmagnetically defined bars. An average height of the bars is less thanabout 50 microns. About eight to about twenty six data bands are presenton the tape.

A tape supply cartridge according to various embodiments has a magneticrecording tape as described herein.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings.

FIG. 1 illustrates a flat-lapped magnetic tape head, in accordance withone embodiment of the present invention.

FIG. 2A is a tape bearing surface view taken from Line 2A of FIG. 1.

FIG. 2B is a detailed view taken from Circle 2B of FIG. 2A.

FIG. 2C is a representative view of a prior art servo pattern.

FIG. 2D is a representative view of a prior art servo pattern accordingto one embodiment of the present invention.

FIG. 2E is a comparative view of a prior art element array relative totwo element arrays according to embodiments of the present invention.

FIG. 3A is a partial view of a writer array in a magnetic tape headaccording to one embodiment of the present invention.

FIG. 3B is a partial view taken along Line 3B-3B of FIG. 3A.

FIG. 4 is a partial view of a writer according to one embodiment of thepresent invention.

FIG. 5 is a partial plan view of an illustrative embodiment of thepresent invention having piggybacked readers and writers.

FIG. 6 is a side view of a tape head having three modules according toone embodiment of the present invention.

FIGS. 7A and 7B illustrate a writer 8 according to another embodiment ofthe present invention.

FIG. 8 is a schematic diagram of a tape drive system according to oneembodiment of the present invention.

DETAILED DESCRIPTION

The following description is the best mode presently contemplated forcarrying out the present invention. This description is made for thepurpose of illustrating the general principles of the present inventionand is not meant to limit the inventive concepts claimed herein.Further, particular features described herein can be used in combinationwith other described features in each of the various possiblecombinations and permutations.

The embodiments described below disclose a new tape format and headdesign.

FIG. 1 illustrates a flat-lapped bi-directional, two-module magnetictape head 100, in accordance with one embodiment of the presentinvention. As shown, the head includes a pair of bases 102, eachequipped with a module 104. The bases may be “U-beams” that areadhesively coupled together. Each module 104 includes a substrate 104Aand a closure 104B with readers and writers 106 situated therebetween.In use, a tape 108 is moved over the modules 104 along a tape bearingsurface 109 in the manner shown for reading and writing data on the tape108 using the readers and writers 106. Conventionally, a partial vacuumis formed between the tape 108 and the tape bearing surface 109 formaintaining the tape 108 in close proximity with the readers and writers106.

FIG. 2A illustrates the tape bearing surface 109 of one of the modules104. A representative tape 108 is shown in dashed lines. The module islong enough to be able to support the tape as the head steps betweendata bands.

A preferred embodiment of the tape 108 includes 12-22 data bands, e.g.,with 16 data bands and 17 servo tracks 202, as shown in FIG. 2A on aone-half inch wide tape. The data bands are defined between servo tracks202. Each data band may include a number of data tracks, for example 96data tracks (not shown). During read/write operations, the elements 106are positioned within one of the data bands. Outer readers, sometimescalled servo readers, read the servo tracks 202. The servo signals arein turn used to keep the elements 106 aligned with a particular trackduring the read/write operations. Typically, a coarse positioner (wormgear, etc.) places the head generally adjacent a given data track, thena fine positioner (voice coil, etc.) keeps the heads aligned using theservo tracks.

Though the number of servo tracks 202 is large, the width of a givendata band is small, and so the width of each servo track iscorrespondingly small. Though intuitively more servo tracks would beexpected to use more tape area, this reduction in data band width andservo track width actually gives more area on tape for data tracks.Thus, the embodiment shown in FIG. 2A provides a net data capacity gainof a few percent over a present LTO tape having four data bands and fiveservo tracks.

A typical servo track, shown in FIG. 2C, includes repeating servopatterns 240. A typical servo pattern 240 includes amagnetically-defined base set 242 (e.g., in a chevron shape: / \) of twoor more magnetically-defined bars 244, which are typically writtenconcurrently. Servo patterns 240 may include groups of the base sets 242nested with one another (e.g., /// \\\). In one embodiment of thepresent invention, the height (H_(b)) of the bars 244 in the servopattern are reduced by about a factor of four or more from servo patterndata currently in commercial use in, e.g., LTO-compliant products. Inone illustrative embodiment, shown in FIG. 2D, the average height(H_(b)) of the bars 254 in the servo pattern 250 are reduced from about190 microns to less than about 50 microns. In one embodiment, the heightof the bars 254 is about 40 microns. This has the effect of providingmore accuracy, as the patterns 250 repeat more frequently. Note that thechevron-type servo pattern is but one of many that can be used in thepresent invention. Other illustrative servo patterns include “M” type/\/\, |\/|, /|\, etc.), “N” type (/\/,|\|, /|/, etc.), etc. The M or Ntype patterns may be preferable to a simple two-bar chevron type servopatterns in some instances, such as where the N or M pattern containparallel bars, thereby allowing the system to accurately calculate avelocity of the tape.

Variations and combinations of the foregoing types of servo base setsare also possible. Also note that the bars need not all have identicaldirect or inverse angles.

In various embodiments, the chevron angle α (defined between adjacentbars of differing directions) is increased, thereby allowing a fasterservo pattern repetition rate. For example, one embodiment increases thechevron angle from the current 6 degrees to about 10-25 degrees, ormore.

The servo patterns are preferably written at a high linear density, suchthat a 4× improvement in servo linear density over current LTO productsis achieved.

The servo track may have data embedded or encoded therein. Such data mayinclude data for encryption, for ascertaining a longitudinal positionalong the tape, etc.

The small width of the data bands also provides more immunity toread/write problems associated with tape dimensional instability, i.e.,lateral expansion. For example, as mentioned above, current LTOexperiences a lateral expansion of 3 μm per data band, which the tapedrive must be designed to handle. The smaller widths of the data bandspresented herein reduce the lateral expansion to about 0.5 to 0.7 μm perdata band.

FIG. 2B depicts a plurality of read and/or write elements 106 formed ina gap 208 on the module 104 of FIG. 2A. As shown, the array of elements106 includes, for example, 16 writers 209, 16 readers 210 and two servoreaders 212, though the number of elements may vary. Illustrativeembodiments include 8, 16, 32, and 40 elements per array 106. Apreferred embodiment includes 24 readers per array and/or 24 writers perarray. This allows the tape to travel more slowly, thereby reducingspeed-induced tracking and mechanical difficulties. While the readersand writers may be arranged in a piggyback configuration as shown inFIG. 2B, the readers 210 and writers 209 may also be arranged in aninterleaved configuration. Alternatively, each array of elements 106 maybe readers or writers only, and the arrays may contain one or more servoreaders. As noted by considering FIGS. 1 and 2A-B together, each module104 may include a complementary set of elements 106 for such things asbi-directional reading and writing, read-while-write capability, etc.

In preferred embodiments, the width of the servo head is such thattransition broadening effects are minimized. Giant Magnetoresistive(GMR) and Tunneling Magnetoresistive (GMR) devices are preferably usedin servo readers for advanced formats which require servo readers havingsmall track widths such as 0.5 micrometers.

According to one embodiment, the head elements are positioned such thatthe span between the outermost servo elements is reduced approximately afactor of 2 to 6 compared to the present LTO servo span. The span isreduced approximately a factor of 5.4 in a preferred embodiment. Theservo span reduction factor is approximately the track pitch improvementfactor. Thus, reducing the span a factor of about 5 by scaling givesapproximately a factor of 5 increase in the maximum number of tracks ona tape before lateral instability limits track density. The writers aredesigned to accommodate the new pitch and are described in detail below.

FIG. 2E illustrates the relative sizes of a current LTO element array260 and element arrays 262 according to one embodiment of the presentinvention. As shown, the servo-to-servo reader span (S₁ to S₂) of array260 is 5.4× the servo-to-servo reader span (S₁ to S₂) of array 262. Aswill be clear to those skilled in the art of magnetic head design, thenew arrays described herein present space limitation challenges notencountered in conventional head design.

The servo-to-servo reader span in a linearly-aligned 16-writer array invarious embodiments of the present invention may be less than about 1.5mm, and in some embodiments may be less than about 1 mm, less than about0.75 mm in other embodiments, and less than about 0.5 mm in yet otherembodiments. The writer pitch in some embodiments is between about 15and about 45 microns. For instance, in one contemplated design, thewriter pitch is between about 31 and about 33 microns. In anothercontemplated design, the writer pitch is between about 28 and about 29microns.

In order to achieve this order of span and/or pitch reduction ascompared to conventional state of the art systems, the inventors wererequired to proceed counter intuitively and contrary to accepted wisdomin the art on several fronts. Instances where the inventors deviatedfrom accepted wisdom are presented below.

In known “pancake” type writers, the width of the back gap is generally3× or more greater than the track width defined at the front gap. Thisdesign minimizes reluctance in the back gap, which improves writingefficiency and enables required magnetic flux to reach the recording gapbefore magnetically saturating the back gap. Accordingly, all known tapehead designers have adopted designs where the back gap width is greaterthan about 3× the front gap width. However, this design places limits onthe write pitch and thus minimum width of the writer array. Forinstance, the servo-to-servo reader span in a 16-writer array in LTOcurrent products is about 2.9 mm.

Further compounding the problem, when writers are too close together,they may magnetically couple together. This phenomenon is sometimesreferred to as writer coupling. In brief, when write coupling occurs,the field generated in one writer causes a field to be generated in thepoles of an adjacent writer, thereby potentially causing writing of“ghost” transitions that may lead to readback noise. Conventional wisdomhas been to space the writers sufficiently so that write coupling isnonexistent.

The inventors have found that by dramatically reducing the back gapwidth relative to the front gap width, in combination with a coilredesigned as set forth below, the close writer spacing required toachieve the small writer pitch is obtainable without causingunacceptable write coupling.

Referring to FIG. 3A, two pancake-type writers 300 of a linear array ofwriters are shown, according to one embodiment of the present invention.Each writer 300 has first and second poles 302, 304. Each pole 302, 304has at least one pole tip positioned towards the tape bearing surface306 of the head. Note that while the term “tape bearing surface” appearsto imply that the surface facing the tape is in physical contact withthe tape bearing surface, this is not necessarily the case. Rather, itis more typical that a portion of the tape is in contact with the tapebearing surface, constantly or intermittently, other portions of thetape ride above the tape bearing surface on a layer of air, sometimesreferred to as an “air bearing”.

As shown in FIG. 3B, a front gap 307 is defined between the pole tips302, 304. Referring again to FIG. 3A, a back gap 308 is defined along anelectrical coupling of the poles 302, 304 at portions thereof positionedaway from the tape bearing surface 306. Widths, of the front and backgaps 307, 308 are defined in a direction parallel to the tape bearingsurface 306 and parallel to planes of deposition thereof. Each writer300 also includes a coil 310. The coil in one contemplated embodimentincludes 10-14 turns, with 10-12 being preferred.

The ratio between the back gap width W_(B) and front gap width W_(F)(e.g., back gap width to upper pole width in front gap) is less than 3:1and preferably less than about 2.5:1, more preferably less than about1.5:1, and in some embodiments between about 1.5:1 and about 0.9:1. FIG.4 illustrates a writer 300 having a back gap width W_(B) to front gapwidth W_(F) ratio of about 1:1. Illustrative embodiments have a frontgap width W_(F) of about 2 to about 10 microns, with a written trackwidth on tape of about 0.5 to about 10 microns (depending on whether ornot the tracks are shingled).

Because the back gap width W_(B) is relatively smaller, the diameter ofthe coil 310 across the back gap 308 and parallel to the tape bearingsurface 306 is reduced, thereby enabling minimum writer pitch. Couplingbetween writer coils may be further reduced by tapering the footprint ofthe coils away from the back gap, as shown in FIG. 5. At the same timethe coil windings can be broadened to minimize coil resistance withoutaffecting the cross-talk between writers. This in turn allows thewriters 300 to be spaced closer together without incurring unacceptablelevels of writer coupling. Additionally, the coil 310 of each writer 300is designed to provide adequate flux while maximizing the distance ofclosest approach of adjacent coils. Coil parameters include coil aspectratio, coil thickness, and distance between adjacent coils.

To further reduce the effects of write coupling, the writer pitch may bemodified to further maximize the distance of closest approach ofadjacent coils.

The narrower widths of the poles 302, 304 behind the front gap alsoprovides less surface area for flux to jump between the poles, therebyimproving writing accuracy and reliability.

The coil is preferably stacked in two or more layers. This provides twoadvantages. First, the yoke length may be shortened. This results inless eddy current slowing of the field rise time, which in turn resultsin faster writing response time. Second, the parasitic reluctance isimproved by decreasing the area covered by the coil and increasing thedistance between the poles. Lower stray reluctance gives higher overallefficiency and thus generally lower write currents. Lower write currentsresult in less cross talk between writers. In addition, back gapseparation is avoided.

The inventors have created prototype heads having the some of theaforementioned dimensions, and have found the heads to write sharptransitions efficiently. The heads also provided several surprising andunexpected results. One such result is that the head provided sharpertransitions of written data than state of the art heads. Another suchresult is that the head provided better overwrite performance than stateof the art heads. Yet another such surprising and unexpected result isthat the head provided better write equalized resolution than state ofthe art heads.

FIG. 5 depicts an illustrative 16 channel R/W array 106 according to oneillustrative embodiment. As shown, the data readers 210 (R1, R2 . . . )are offset from the writers 209 (W1, W2 . . . ). Servo readers 212(Servo) are also present.

Another way to build the head is to have the functions of reading andwriting performed on different modules. As shown in the write-read-write(W-R-W) head 600 of FIG. 6, outer writing modules 602, 604 flank asingle reading module 606. As the names imply, the outer modules 602,604 include two or more arrays of writers in a configuration, forexample, as shown in FIG. 3A. With continued reference to FIG. 6, thereading module 606 includes two or more arrays of readers. The modules602, 604, 606 are offset and set in relationship with each other suchthat internal wrap angles are defined between the modules 602, 604, 606.Cables 609 connect the elements to a controller.

In this embodiment, the tape bearing surfaces of the modules may lie onparallel or nearly parallel planes, but are offset in a directionperpendicular to the planes. When the tape 608 moves across the head 600as shown, air is skived from below the tape 608 by a skiving edge 610 ofthe first outer writing module 602, and instead of the tape 608 liftingfrom the tape bearing surface 612 of the first outer module 602 (asintuitively it should), the reduced air pressure in the area between thetape 608 and the tape bearing surface 612 allow atmospheric pressure tourge the tape towards the tape bearing surface 612. The trailing end 620of the outer writing module 602 (the end from which the tape leaves theouter writing module 602) is proximate to the reference point whichdefines the wrap angle over the tape bearing surface of the innerreading module 606. The same is true of the other outer writing module604 when the tape travel direction is reversed.

Variations on the head 600 of FIG. 6 include a R-W-R head, a R-R-W head,a W-W-R head, etc. For example, in a R-W-R head, the outer modules 602,604 perform reading while the middle module 606 performs writing. In aR-R-W head, the leading module 602 and middle module 606 perform readingwhile the trailing module 604 performs writing. In a W-W-R head, theleading module 602 and middle module 606 perform writing while thetrailing module 604 performs reading. Again, the leading and trailingmodules 602, 604 may operate concurrently with each other and the middlemodule 606, may operate individually, or may operate in combinations oftwo modules.

FIGS. 7A and 7B illustrate a writer 209 according to another embodimentof the present invention. As shown, the writer 209 is a solenoid coiltype writer. The coil 310 wraps around the upper pole 302.

In another embodiment, the coil wraps the bottom pole. In yet anotherembodiment, the coils wrap both poles in a double helix configuration.

FIG. 8 illustrates a simplified tape drive which may be employed in thecontext of the present invention. While one specific implementation of atape drive is shown in FIG. 8, it should be noted that the embodimentsof the previous figures may be implemented in the context of any type oftape drive system.

As shown, a tape supply cartridge 820 and a take-up reel 821 areprovided to support a tape 822. These may form part of a removablecassette and are not necessarily part of the system. Guides 825 guidethe tape 822 across a preferably bidirectional tape head 826, of thetype disclosed herein. Such tape head 826 is in turn coupled to acontroller assembly 828 via a write-read cable 830. The controller 828,in turn, controls head functions such as servo following, writing,reading, etc. An actuator 832 controls position of the head 826 relativeto the tape 822.

A tape drive, such as that illustrated in FIG. 8, includes drivemotor(s) to drive the tape supply cartridge 820 and the take-up reel 821to move the tape 822 linearly over the head 826. The tape drive alsoincludes a read/write channel to transmit data to the head 826 to berecorded on the tape 822 and to receive data read by the head 826 fromthe tape 822. An interface is also provided for communication betweenthe tape drive and a host (integral or external) to send and receive thedata and for controlling the operation of the tape drive andcommunicating the status of the tape drive to the host, all as will beunderstood by those of skill in the art.

One skilled in the art will appreciate that the dimensions given aboveand other places herein are presented by way of example only and can bemade larger or smaller per design and fabrication constraints,performance considerations, etc.

Any of the above embodiments or combinations of portions thereof canalso be applied to any type of tape head and magnetic tape recordingsystems, both known and yet to be invented. For example, the teachingsherein are easily adaptable to interleaved heads, which typicallyinclude opposing modules each having an array of alternating readers andwriters configured to provide read-while-write capability.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A magnetic recording tape, comprising: at leastabout eight data bands, wherein each data band is defined between a pairof adjacent servo tracks, each pair of adjacent servo tracks definingonly a single data band therebetween, wherein one of the servo trackshas data encoded therein, the data including data for encryption,wherein each servo track comprises a series of base sets of themagnetically defined bars, each base set comprising at least one of: atleast three bars in an “N” type servo pattern, and at least four bars inan “M” type servo pattern.
 2. The magnetic recording tape as recited inclaim 1, wherein one of the servo tracks has data encoded therein forascertaining a longitudinal position along the tape.
 3. The magneticrecording tape as recited in claim 1, wherein each servo track comprisesa series of base sets of magnetically defined bars, each base setcomprising at least three bars.
 4. The magnetic recording tape asrecited in claim 1, wherein each servo track comprises a series ofmagnetically defined bars, wherein an angle between at least some of thebars is between about 10 degrees and about 25 degrees.
 5. The magneticrecording tape as recited in claim 1, wherein a distance between theservo tracks is less than about 1.5 mm.
 6. The magnetic recording tapeas recited in claim 1, wherein the distance between the servo tracks isless than about 0.75 mm.
 7. A tape cartridge having the magneticrecording tape as recited in claim
 1. 8. A magnetic recording tape,comprising: a plurality of servo tracks, each servo track comprising aseries of magnetically defined bars, wherein an average height of thebars is less than about 50 microns, wherein about eight to about twentysix data bands are present on the tape, wherein each servo trackcomprises a series of base sets of the magnetically defined bars, eachbase set comprising at least one of: at least three bars in an “N” typeservo pattern, and at least four bars in an “M” type servo pattern. 9.The magnetic recording tape as recited in claim 8, wherein each servotrack comprises the base set comprising at least three bars in an “N”type servo pattern.
 10. The magnetic recording tape as recited in claim8, wherein a distance between the servo tracks is less than about 1.5mm.
 11. The magnetic recording tape as recited in claim 8, wherein thedistance between the servo tracks is less than about 0.75 mm.
 12. Themagnetic recording tape as recited in claim 8, wherein one of the servotracks has data encoded therein, the data being selected from a groupconsisting of data for encryption and data for ascertaining alongitudinal position along the tape.
 13. The magnetic recording tape asrecited in claim 8, wherein each servo track comprises the base setcomprising at least four bars in an “M” type servo pattern.
 14. A tapecartridge having the magnetic recording tape as recited in claim
 8. 15.The magnetic recording tape as recited in claim 8, wherein the tape haseight to twenty two data bands, wherein each data band is definedbetween a pair of adjacent servo tracks, each pair of adjacent servotracks defining only a single data band therebetween.
 16. The magneticrecording tape as recited in claim 1, wherein a number of the data bandson the tape is from eight to twenty two.
 17. The magnetic recording tapeas recited in claim 1, wherein each servo track comprises the base setcomprising at least three bars in an “N” type servo pattern.
 18. Themagnetic recording tape as recited in claim 1, wherein each servo trackcomprises the defined bars comprising at least four bars in an “M” typeservo pattern.